1setmclk(1) Svgalib User Manual setmclk(1)
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6 setmclk - adjust the memory timing of certain Cirrus cards.
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9 setmclk
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13 This program sets the memory clock of Cirrus 5424/26/28 cards.
14 The first three values could be set by utility programs that came with
16 my card (AVGA3), but somewhat higher values seem to work (on my card at
17 least). It may be that better and more recent Cirrus cards use a higher
18 value as boot-up default. It should depend on DRAM speed, but it seems
19 to be more dependant on the card logic.
20 I have the impression that many Cirrus 542x cards suffer from horrible
22 BIOS version/DRAM timing misconfigurations. Perhaps even some versions
23 of MS-Windows drivers change the MCLK register. In any case, the boot-
24 up BIOS default (0x1c) may be inappropriately low for the type of DRAM
25 timing most cards use.
26 Using a higher memory clock gives a very significant performance
28 improvement; with high dot clock modes (like 640x480x16M or
29 1150x900x256) performance can be more than twice that of the standard
30 50 MHz clock. This goes for both (VLB) framebuffer access and acceler‐
31 ated features (bitblt). This also helps XFree86 server performance, but
32 only if the XFree86 Cirrus driver doesn't set the memory clock register
33 (it should work for XFree86 1.3 and 2.0). Use at your own risk!
34 Note that the dot clock is something entirely different. There does not
36 seem to be much correlation between the two (i.e. if a high dot clock
37 gives screen problems, using a high memory clock is not likely to fix
38 it, other than improving speed).
39 The actual memory clock is hard compiled into the program. It defaults
41 to 0x1c. You can change this value and some suggestiong come in th
42 source of the utility.
43 This utility is part of svgalib and can be found in the utils/ subdi‐
45 rectory of the original svgalib distribution. However, it is not
46 installed by default, s.t. it is unclear where you can find it if your
47 svgalib was install linux distribution.
48 In case of any such problem, simply get an svgalib distribution from
50 the net. You don't need to install it. Just make in the utils/ subdi‐
51 recty. As of this writing, svgalib-1.2.12.tar.gz is the latest version
52 and can be retrieved by ftp from sunsite.unc.edu at
53 /pub/Linux/libs/graphics and tsx-11.mit.edu at /pub/linux/sources/libs
54 which will most probably be mirrored by a site close to you.
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58 svgalib(7), vgagl(7), libvga.config(5), convfont(1), dumpreg(1),
59 restorefont(1), restorepalette(1), restoretextmode(1), runx(1),
60 savetextmode(1), fix132x43(1), textmode(1).
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64 This manual page was edited by Michael Weller <eowmob@exp-math.uni-
65 essen.de>. The exact source of the referenced utility as well as of the
66 original documentation is unknown.
67 It is very likely that both are at least to some extent are due to Harm
69 Hanemaayer <H.Hanemaayer@inter.nl.net>.
70 Occasionally this might be wrong. I hereby asked to be excused by the
72 original author and will happily accept any additions or corrections to
73 this first version of the svgalib manual.
74Svgalib (>= 1.2.11) 2 Aug 1997 setmclk(1)